Check the voltage drop on a DC run, or let it pick the smallest conductor that stays under the limit. Built for 12 / 24 / 48 V marine and off-grid systems.
Voltage drop is only half of cable sizing — the conductor also has to carry its fuse. The designer does both for every run in your system, then draws the diagram.
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Voltage drop is the voltage lost to the resistance of the cable, there and back. It rises with current and length and falls as the conductor gets thicker. The usual limits are 3% for critical runs (feeders, panels, sensitive electronics) and 10% for non-critical ones (lighting, accessories).
Lower-voltage systems suffer most: the same watts at 12 V draw four times the current of 48 V, so 12 V runs are almost always sized by voltage drop rather than ampacity. The coefficients here come from IEC 60228 and include the round trip — enter the one-way length.
3% for critical circuits (main feeders, solar, electronics) and up to 10% for non-critical ones like lighting. The calculator defaults to 3%.
For the same power, current is inversely proportional to voltage, and drop scales with current — so a 12 V run carries 4x the current (and far more drop) of the same load at 48 V.
One-way. The coefficient already accounts for the current flowing out and back.
Wattonomy applies these standards in its calculations. It is not certified, sponsored or endorsed by ABYC, ISO, NFPA or Victron. Last reviewed June 2026 — see the methodology.
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